Shielded conductor for disk windings of inductive devices

ABSTRACT

A shielded conductor used with disk windings for inductive devices characterized in that the disk windings comprise a plurality of coil units of conductive material wound in disk form, the disk windings having at least several coil units nearer to its external line terminal holding therein at least a winding of the shielded conductor with its inner end open so as to maintain the shielded conductor at a predetermined potential, a member material for regulating the electric field is connected to the open inner end of the shielded conductor, and an insulating layer is covered on both the connection and the member material for regulating the electric field. The member material for regulating the electric field permits the alleviation of concentration of electric field at the open inner end of the shielded conductor thereby to prevent dielectric breakdown between the coil units and the shielded conductor.

United States Patent [191 Ohta et al.

[11] 3,820,048 [4 June 25, 1974 SHIELDED CONDUCTOR FOR DISK WINDINGS OF INDUCTIVE DEVICES [75] Inventors: Kazuo Ohta; Kentaro Kurita;

Shigeru Morita, all of Hitachi, Japan [73] Assignee: Hitachi, Ltd., Tokyo, Japan [22] Filed: June 1, 1973 [211 App]. No.: 366,146

[30] Foreign Application Priority Data Primary Examiner-Thomas J. Kozma Attorney, Agent, or FirmCraig and Antonelli [57] ABSTRACT A shielded conductor used with disk windings for inductive devices characterized in that the disk windings comprise a plurality of coil units of conductive material wound in disk form, the disk windings having at least several coil units nearer to its external line terminal holding therein at least a winding of the shielded conductor with its inner end open so as to maintain the shielded conductor at a predetermined potential, a member material for regulating the electric field is connected to the open inner end of the shielded conductor, and an insulating layer is covered on both the connection and the member material for regulating the electric field. The member material for regulating the electric field permits the alleviation of concentration of electric field at the open inner end of the shielded conductor thereby to prevent dielectric breakdown between the coil units and the shielded conductor.

6 Claims, 14 Drawing Figures PATENTEnJunzs 1924 SHEET 3 UF 4 Y FIG. 6A

FIG. 7

FIG. 8A

m minmzs 1974 I $820,048

saw u or 4 FIG. 9

FIG l0 FIG. llB

BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to a shielded conductor used with the disk windings of such electrically inductive devices as transformers and reactors for enlarging the series electrostatic capacitance of the disk windings thereby to improve the impulse-voltage characteristics of the disk windings.

2. Description of the Prior Art It is well known that the application of an impulse voltage such as a lightning surge or switching surge to the windings of electrical inductive devices including the transformer and reactor causes oscillation of potential thereof, which may lead to the dielectric breakdown of the windings in an extreme case. A method generally employed to improve the impulse voltage characteristics of the windings of inductive devices is to make larger the series capacity of the windings than the earth capacity thereby to obtain a substantially uniform potential distribution in the windings as a whole.

Disk windings of a high mechanical strength are widely used for the high-voltage windings of inductive devices such as transformers and reactors. The disk windings comprise a plurality of sequentially seriesconnected coil units of disk form, each of which, in turn, consists of a disk comprising predetermined turns of a rectangular flat wire of conductive material covered with an insulating material or a plurality of enamel-covered thin rectangular fiat wires stranded into a transposed cable with an insulating covering thereon.

The disk windings, however, have the disadvantage that inferior impulse voltage characteristics result from the relatively small opposing area of the coil units, the multiplicity of the coil units and hence small series electrostatic capacity between the coil units.

In an attempt to overcome the above-mentioned disadvantage, the method has been suggested in US. Pat. No. 3,160,838 and 3,560,902 such that thin shielded conductors are wound in at least several coil units nearer to the external line terminal among the pluraliry of coil units constituting the disk windings, thereby to increase the series electrostatic capacity of the windings. Each of the shielded conductors is covered with an insulating material and wound at least by a turn be tween the conductive materials constituting each coil unit, while the inner end of the shielded conductor is kept open. The outer end of the shielded conductor is connected with another shielded conductor in the adjacent coil unit or in a farther coil unit more than several units away or with a given coil unit itself thereby to maintain an appropriate electric potential. In this way, the coil units at some distance from each other are connected electrostatically, and the direction of charge current due to the impulse voltage flowing between the adjacent conductive materials or between a conductive material and a shielded conductor is reversed, whereby the inductance therebetween is eliminated to add a large series electrostatic capacity between the coil units.

In the above-mentioned method, the series electrostatic capacity of the disk windings is regulated according to the number of turns by which the shielded conductor is wound in the coil unit constituting the disk winding or according to the manner in which the coil units involving such shielded conductors are arranged, so that the distribution of electric potential at the time of application of an impulse voltage follows a substantially straight line thereby to improve the electrical characteristics of the windings.

In such disk windings, there occurs a difference of electric potential between the conductive material making up the coil unit and the shielded conductor wound therein, and therefore the conductive material of the coil unit and the shielded conductor are provided with an insulating material covered thereon for the purpose of giving a proper margin for their protection from alternating current and impulse voltage. Since, however, the inner end of the shielded conductor wound in the coil unit is kept open as mentioned above, electric field is concentrated at the particular open inner end of the shielded conductor at the time of energization of the disk windings. This concentration of electric field often gives rise to a dielectric breakdown between the open inner end of the shielded conductor and the conductive material of the coil unit.

The above-mentioned disadvantage is capable of being obviated by covering a thicker insulating material on the conductive material of the coil unit and the shielded conductor. This process, however, adds to another disadvantage of a reduced space factor of the windings of the inductive device involved.

All of the above-mentioned problems result in a reduced reliability of the device and greater complication of the manufacturing processes, and therefore effective solutions are desirable.

SUMMARY OF THE INVENTION Accordingly, it is an object of the invention to provide a method whereby the open inner end of the shielded conductor of the disk windings for inductive devices is easily processed.

Another object of the invention is to alleviate the concentration of electric field at the open inner end of the shielded conductor of inductive devices thereby to prevent dielectric breakdown between the conductive material of the coil unit and the shielded conductor.

A farther object of the invention is to reduce the thickness of the insulating material covered on the conductive material of the coil unit and the shielded conductor by the effective processing of the open inner end of the shielded conductors of windings for inductive devices.

Still another object of the invention is not only to facilitate the manufacture but increase the reliability of the disk winding for inductive devices by employing an effective shielded conductor.

The above-mentioned objects are achieved by the invention according to which the disk windings for inductive devices comprise a plurality of coil units each including a plurality of annular or disk portions covered with an insulating-material, and a shielded conductor covered with an insulating material is wound by at least a turn with its inner end open with at least several coil units nearer to the terminal of the windings connected to an external line, thereby to maintain a predetermined electric potential, characterized in that a bandshaped member material for regulating the electric field is fixed on the open inner end of the shielded conductor and an insulating material is covered on both the fixed connection and the member material for regulating the electric field.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is a partly broken side view of an inductive device to which the shielded conductor according to the invention is effectively applied.

FIGS. 2, 3 and 4 are sectional view showing part of different disk windings for inductive devices employing the shielded conductor according to the invention.

FIG. 5 is a plan view of the different disk windings for inductive devices shown in FIGS. 2, 3 and 4 viewed from the respective external line terminals thereof.

FIG. 6A is a diagram showing a front view of the open inner end of the shielded conductor for the disk windings of an inductive device to which the present invention is applied.

FIG. 6B is a sectional view taken in line VI--VI in FIG. 6A.

FIG. 7 is a diagram showing a front view of the shielded conductor according to the present invention with the insulating covering removed from its open inner end.

FIG. 8A is a diagram showing a front view of the member material for regulating electric field provided at the open inner end of the shielded conductor according to the invention.

FIG. 8B shows a plan view of the member material of FIG. 8A.

FIG. 9 is a front view showing an example of how the member material for regulating the electric field is connected to the shielded conductor with the insulating material removed at its open inner end.

FIG. 10 is a plan view showing another example of how the member material for regulating the electric field is connected to the shielded conductor with the insulating materialremoved from its open inner end.

FIG. 11A is a front view showing an example of application of the insulating material, shown cut away, to the connection between the shielded conductor and the member material for regulating the electric field illustrated in FIG. 8.

= FIG. 1 1B shows a plan view of the connection of FIG. 11A with the insulating material cut away.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The shielded conductor for the disk windings of inductive devices according to the present invention will be now explained with reference to the accompanying drawings.

Referring to FIG. 1, an example of core-type inductive device is shown comprising an iron core 21 having main core portions around which coils are wound, lowvoltage windings 22 and high-voltage windings 23 which are arranged concentrically. Symbols U and N show the external line and neutral terminals of the high-voltage windings 23 respectively. In an ordinary transformer, the low-voltage windings 22 consist of helical coils, while the high-voltage windings 23 are made up of disk windings including a plurality of coil units, the external line terminal U and the neutral terminal N being generally taken out from the upper and lower ends thereof.

As shown in FIGS. 2, 3 and 4, the high-voltage windings 23 generally comprise well known conductive materials 31 with an insulating material (not shown) covered thereon which are wound into a plurality of disk coil units a, b, c, These coil units are connected in series with adjacent ones alternately at their inside and outside portions in order of the numerals attached to the conductive materials by the agency of the connecting means 32. In the high-voltage disk windings shown above, the shielded conductor 33 with its inner end 33A open as shown in FIG. 5 and covered with an insulating material (not shown) is wound between the successive conductive materials 31 of at least several ones of the coil units nearer to the external line terminal U by at least a turn, and the shielded conductors 33 with its outer end 333 thus wound in are connected with each other by means of lead wires 34 as shown in the drawings, thereby to maintain a predetermined electric potential. In this way, the disk windings hold a sufficient amount of series electrostatic capacity for improved electric characteristics against an impulse voltage that may be applied.

As mentioned above, the shielded conductor 33 is covered with an insulating material of a predetermined thickness. However, in view of the fact that the inner end of the shielded conductor 33 wound in the coil units is kept open while holding an electric potential, an electric field is concentrated at the open inner end 33A, and therefore there is a great likelihood of dielec tric brakdown in spite of the conductive material 31 and shielded conductor 33 being covered with an insulating material as a protection from alternating and impulse voltages.

In order to avoid such as undesirable situation, the open inner end of the shielded conductor for the disk windings of an inductive device which is wound in the coil unit is constructed as shown in FIGS. 6A and 6B. The forward portion of the open inner end of the shielded conductor 33 with the length of 1 is exposed without being covered with the insulating material 40 and thereby a portion in the shape of a bamboo shoot with the length of l is formed. The exposed portion of the shielded conductor 33 is electrically connected with a member material 50 for regulating electric field with the length of L, the member material 50 and being made in the manner as mentioned later, and the connection and the electric-field regulating member material 50 is wound in craft paper or the like to form an insulating covering 60 of a predetermined thickness.

The provision of the electro-field regulating member material 50 alleviates the concentration of electric field at the open inner end of the shielded conductor 33, so that any case of dielectric brakdown between the conductive materials making up the coil unit and the shielded conductor is prevented thereby greatly increasing the breakdown voltage of the device.

Craft paper 41 or similar material constituting the insulating covering 40 is wound back on the shielded conductor 33 in such a manner as shown in FIG. 7 to expose the most forward portion of the open inner end thereof. The tip of the exposed open inner end of the shielded conductor 33 to be connected to the member material 50 is rounded with an appropriate radius R in order to achieve improved alleviation of the concentration of electric field thereat. For the shielded conductor with the width W of 10 mm, for example, a suitable radius R may be approximately 5 mm. Also, the exposed open inner end of the shielded conductor may be made as long as 40 mm, while the length l, of the portion of the insulating covering in the shape of a bamboo shoot may be so selected as to be 1.5 times that of the length 1 of the exposed open inner end of the shielded conductor 33, thereby to make possible effective reinsulation.

The member material 50 for regulating electric field comprises resistor sections and an insulator section with the length of the resistor sections having the length equal to the sum of l and The resistor sections are made progressively higher in resistance sections are made progressively higher in resistance from portions 1 to l, and are electrically connected with the open inner end of the shielded conductor 33 to alleviate the concentration of electric field. In order for the electric-field regulating member material 50 to be made progressively higher in resistance from its side connected with the shielded conductor 33, as shown in FIGS. 8A, and 88, a low-resistance semiconductive material 52 and a high-resistance semiconductive material 53 are painted to the lengths of I and 1 respectively and dried with portions thereof overlapped on each other, the remaining portion as long as 1 being left unprocessed. Varnish with the resistance of 0.1 to 0.3 Mwand 4,000 to 12,000 M0), for example, are used as the low-resistance and high-resistance semiconductive materials respectively. Many of the member material 50 for regulating the electric field has the length L of 150 to 200 mm, of which the portion as long as 100 mm consists of the resistor sections, the remaining portion making up the insulator section. The ratio of the length of the low-resistance section to that of the high-' resistance section is set approximately at 2 to 1.

In place of varnish employed as above for the member for regulating the electric field, semiconductive paper mixed with carbon which is made on a wet machine or plastic material may be used to achieve the same purpose of progressive increment of resistance.

In the member material for regulating electric field with its resistance thus graded, progressive changes in electric potential up to the tip thereof permits the elimination of concentration of electric field even when it is connected with the shielded conductor.

To achieve as perfect electrical connection as possible between the member material 50 and the shielded conductor without the insulating covering 40 on one hand and to facilitate engagement therebetween on the other, the end of the member material 50 nearer to the shielded conductor 33 is provided with a forked portion 54, as shown in FIG. 8B, which is painted with the above-mentioned low-resistance semiconductive material. The forked portion 54 supports between its prongs the open inner end of the shielded conductor 33 thereby to achieve improved electrical connection.

For improved electrical connection between the shielded conductor 33 and the member material 50 for regulating electric field, it is recommended that, as shown in FIG. 10, the connecting tape 55 comprising craft paper or other thin insulating paper painted with the above-mentioned low-resistance semiconductive material be interposed between the shielded conductor and the member material 50. The connection between the shielded conductor 33 and the member material 50 is fixed with the insulating tape 56 shown in a dashed line, as shown in FIGS. 9, l0, and then insulating paper like craft paper is wound on the connection, the member material 50 for regulating electrical field and the end portion of shielded conductor 33 in the shape of a bamboo shoot, thereby to complete the insulating covering 60 of a required thickness.

The insulating covering 60 is wound in such a manner as to form an end portion in the shape of bamboo shoot which extends an additional length of 1 from the member material 50. To facilitate the process of forming the end portion in the shape of bamboo shoot, a guide press board 61 or the like is attached provisionally to the end of the member material 50, as shown in FIGS. 11A and 11B, and this guide board is utilized to wind the insulating paper into the insulating covering 60. Subsequent to the forming of the insulating covering 60, the guide board 61 is extracted, thereby to complete the shielded conductor for disk windings used with electrical inductive devices according to the invention.

The shielded conductor for the disk windings of the inductive devices thus completed is used, as in the conventional ones, in the coil unit with its inner end kept open, the only difference residing in the fact that according to the invention the provision of the member material for regulating the electric field effectively alleviates the concentration of electric field, with the result that the occurrence of dielectric breakdown between the coil unit and the shielded conductor is prevented and at the same time the breakdown voltage thereof is increased for improved reliability of the windings. Further, the insulating covering of the coil unit and the shielded conductor is made thinner than that of the conventional devices, resulting in an improved space factor of the windings and a smaller size of the device.

It is needless to say that the shielded conductor for the disk winding of the inductive devices according to the present invention is applied not only to the shown disk windings but also to all the disk windings for the inductive devices requiring shielded conductors, and in such cases the same advantages as mentioned above are achieved by arranging the shielded conductor at least in those coil units nearer to an external line terminal.

We claim:

1. In a disk winding for electrical inductive device comprising a plurality of coil units of conductive material connected in series with each other and shielded conductors with an inner end kept open, said conductive material of each of said coil unit being covered with an insulating material and wound into the shape of a disk, said shielded conductors being covered with an insulating material and wound by at least a turn in at least several coil units nearer to an external line terminal thereby to maintain a predetermined electric potential; the improvement wherein said shielded conductors comprise a band-shaped member material for regulating electric field fixedly connected to said open inner end, an insulating material being covered on said connection and said member material for regulating electric field.

2. Shielded conductors for disk windings of inductive devices according to claim 1, in which said bandshaped member material for regulating electric field comprises a plurality of resistor sections connected to the open inner end of said shielded conductors and an insulator section.

3. Shielded conductors for disk windings of inductive devices according to claim 1, in which said member material for regulating electric field comprises a bandshaped insulating material which is covered with predetermined lengths of a low-resistance semiconductive paint and high-resistance semiconductive paint in that order from the side connected with open inner end of the shielded conductors, said band-shaped insulating material further having a predetermined length of unpainted portion, said low-resistance semiconductive paint and said high-resistance semiconductive paint being partly overlapped on each other.

4. Shielded conductors for disk windings of inductive devices according to claim 1, in which that end of said band-shaped member material which is opposed to said shielded conductors is provided with a forked portion covered with said low-resistance semiconductive paint, said forked portion holding between its prongs the open inner end of said shielded conductors, said shielded conductors being fixedlyconnected to said member material by means of an insulating tape.

5. Shielded conductors for disk windings of inductive devices according to claim 1, in which the open inner end of said shielded conductors is connected to said member material for regulating electric field through the interposition therebetween of a connecting tape comprising thin insulating paper painted with a lowresistance semiconductive material.

6. In a disk winding for electrical inductive devices comprising a plurality of coil units of conductive material connected in series with each other and shielded conductors with an inner end kept open, said conductive material which constitutes each of said coil unit being covered with an insulating material and wound into the shape of a disk, said shielded conductors being covered with an insulating material and wound by at least a turn in at least several coil units nearer to an external line terminal thereby to maintain a predetermined electric potential; the improvement wherein the open inner end of said shielded conductors is connected to a member material for regulating electric field fixedly with an insulating tape through the interposition of a connecting tape comprising a thin insulating paper painted with a low-resistance semiconductive material, said member material comprising a bandshaped insulating material including a forked-portion and a predetermined length of unprocessed portion, said forked-portion being painted with a low resistance semiconductive material and supporting the open inner end of said shielded conductors, said member material being painted partly with a predetermined length of a low-resistance semiconductive material and partly with a predetermined length of a high-resistance semiconductive material in that order from that side of said member material provided with said forked portion said low-resistance semiconductive material and said high-resistance semiconductive material being partly overlapped on each other, said connection and said member material being covered with an insulating material. 

1. In a disk winding for electrical inductive device comprising a plurality of coil units of conductive material connected in series with each other and shielded conductors with an inner end kept open, said conductive material of each of said coil unit being covered with an insulating material and wound into the shape of a disk, said shielded conductors being covered with an insulating material and wound by at least a turn in at least several coil units nearer to an external line terminal thereby to maintain a predetermined electric potential; the improvement wherein said shielded conductors comprise a band-shaped member material for regulating electric field fixedly connected to said open inner end, an insulating material being covered on said connection and said member material for regulating electric field.
 2. Shielded conductors for disk windings of inductive devices according to claim 1, in which said band-shaped member material for regulating electric field comprises a plurality of resistor sections connected to the open inner end of said shielded conductors and an insulator section.
 3. Shielded conductors for disk windings of inductive devices according to claim 1, in which said member material for regulating electric field comprises a band-shaped insulating material which is covered with predetermined lengths of a low-resistance semiconductive paint and high-resistance semiconductive paint in that order from the side connected with open inner end of the shielded conductors, said band-shaped insulating material further having a predetermined length of unpainted portion, said low-resistance semiconductive paint and said high-resistance semiconductive paint being partly overlapped on each other.
 4. Shielded conductors for disk windings of inductive devices according to claim 1, in which that end of said band-shaped member material which is opposed to said shielded conductors is provided with a forked portion covered with said low-resistance semiconductive paint, said forked portion holding between its prongs the open inner end of said shielded conductors, said shielded conductors being fixedly connected to said member material by means of an insulating tape.
 5. Shielded conductors for disk windings of inductive devices according to claim 1, in which the open inner end of said shielded conductors is connected to said member material for regulating electric field through the interposition therebetween of a connecting tape comprising thin insulating paper painted with a low-resistance semiconductive material.
 6. In a disk winding for electrical inductive devices comprising a plurality of coil units of conductive material connected in series with each other and shielded conductors with an inner end kept open, said conductive material which constitutes each of said coil unit being covered with an insulating material and wound into the shape of a disk, said shielded conductors being covered with an insulating material and wound by at least a turn in at least several coil units nearer to an external line terminal thereby to maintain a predetermined electric potential; the improvement wherein the open inner end of said shielded conductors is connected to a member material for regulating electric field fixedly with an insulating tape through the interposition of a connecting tape comprising a thin insulating paper painted with a low-resistance semiconductive material, said member material comprising a band-shaped insulating material including a forked-portion and a predetermined length of unprocesSed portion, said forked-portion being painted with a low resistance semiconductive material and supporting the open inner end of said shielded conductors, said member material being painted partly with a predetermined length of a low-resistance semiconductive material and partly with a predetermined length of a high-resistance semiconductive material in that order from that side of said member material provided with said forked portion said low-resistance semiconductive material and said high-resistance semiconductive material being partly overlapped on each other, said connection and said member material being covered with an insulating material. 